Well perforating device



w.'J. swEETMAN WELL PERFORMING DEVICE May `17, 1955 2 Sheets-Sheet lFiled NGV. 14, 1949 ATTORNEY.

May 17, 1955 .w. J. swEl-:TMAN 2,708,408

WELL PERFORMING DEVICE Filed Nov. 14, 1949 2 sheets-sheet 2 IN VEN TOR.William ,ju/admit ATTORNEY Unite This invention relates to perforatingdevices commonly called guns, which are employed to perforate the wallsof wells, such as oil or gas wells, to provide communication between thewell bore and the surrounding formations to permit liow of the formationliuids into the,

well bore, More particularly, this invention is directed to perforatingdevices of the type which employ hollowed explosive charges rather thanthe more conventional bullet-type projectiles as perforating elements.

The cavity or hollow-charge principle has been applied by applicant tothe perforation of the walls of wells and of the metal casings and otherwell bore linings because of the superior penetrating power obtainablewith such charges. For well perforating purposes, such charges wereconstructed in the form of relatively highdensity bodies composed ofhigh-brisance types of detonating explosives, having an end thereoffacing the object to be pierced provided with a cavity or hollow,generally of conical or arcuate shape, which is lined with a thin metalliner. When suitably detonated, the major proportion of the generatedexplosive force is concentrated, by virtue of the shape of the hollowand liner, intoV a relatively narrow gaseous jet of tremendous power andpenetrating force which is directed largely along the longitudinal axisof the hollow. Such perforating charges do not employ projectiles butdepend upon the penetrating power of the gaseous jet to elfect thedesired degree of perforation.

In a hollow charge, the most efficient jet formation l for developingmaximum power is developed by detonating the charge from theV endopposite the hollow and on the axis of the charge. The detonation wavescreated by this arrangement will then travel generally axially of theStates arent charge from the locus of detonation, increasing in power asthey travel through the body of the charge until they reach the hollowedend which will then effectively focus and intensify the explosive forceinto a high powered penetrating jet. The power developed by such acharge is dependent, therefore, in part, at least, upon the length ofthe charge, which, in turn, has an optimum relation to the diameter ofthe charge at the hollowed end. This optimum length is generally fromone to two times the diameter of the charge at the hollowed end. Due

to the space limitations in the ordinary well bore, both the diameterand length of the charges which. may be used are necessarily limited. Inorder, therefore, to obtain maximum penetrating power, applicant hasemployed charges of maximum length within the optimum limits and to`detonate them from the end opposite the hollow to assure high-orderdetonation of the charges and proper jet formation under all conditions.

Moreover, in well perforating, it is generally desirable to make aplurality of perforations through the well bore linings along the faceof the fluid-containing earth formation, in order to` provide aplurality of uid passages from the formation into the well bore toassure access of the formation fluids from the several parts of theformationsY to the well bore.

For the purposes of Y `ice economy and eciency, it is desirable toeffect the dei sired plurality of perforatons in a single operation, andapplicants practice has been to mount a plurality of perforating chargesin a single carrier or gun and set them olf at one time.

Due to the space limitations in the usual relatively narrow well bore itis desirable to provide a series of perforating charges arranged inaxially spaced relation along a carrier and to orient them angularlyabout the longitudinal axis of the carrier. Since, as noted, it isdesirable to employ perforating charges of maximum length and diameterto produce perforations of maximum area and depth of penetration, suchcharges will generally be of a size to extend for substantial lengthstransversely of the carrier, with the hollow at one end from which theperforating jet will emerge to strike the well wall. Moreover, since, asnoted, in order to produce optimum jet formation to elect maximumpenetration, it has been applicants practice to detonate such chargesfrom the ends opposite the hollowed ends, it has been found diticult toprovide a relatively simple, troublefree fuzing arrangement for a stringof such charges which may be tired from one end of the string and whichwill effectively detonate successively all of the charges in the stringat high-order detonation rates and with proper jet formation necessaryto produce maximum penetrating power. In ring a string of charges'soarranged, it becomes highly desirable to provide a relatively simplefuzing arrangement which will detonate all of the charges in rapidsuccession and at the high order detonation rates and with proper jetformation necessary to produce maximum penetration power.

One of the objects of this invention, therefore, is to improve theperforating device in order to secure a more effective operation.

Accordingly, this invention includes the provision of a perforatingdevice comprising a plurality of hollow detonating charges, arranged inan elongated string, and employing a relatively simple and novel form offuzing arrangement for successively detonating the charges at high-orderdetonation rates from a single firing element connected to one end ofthe string; andv in which the several charges are of optimum sizes toproduce relatively large perforations through the well bore and itslinings extending to considerable depth into the surrounding formations.

Applicant provides a perforating unit of standardized form anddimensions containing a single hollow charge, each of said units beingadapted for connection to other similar units to form a string ofcharges of any desired length and in any relative orientations; each ofsaid units having its individual fuzing element for detonating itscharge; and each of said fuzing elements bein,U arranged in a novelmanner relative to said charge to provide for simple and automaticconnections to the fuzing elements of the adjacent units to therebyprovide a continuous detonatable fuzing train for effectively detonatingthe successive charges forming said string from a single firing elementconnected to the upper end of such a string;

Generally stated and in accordance with an illustrative embodiment ofthis invention the perforating device ernbodies a tiring head and acarrier comprising a series of separable perforating units. Theperforating units are of substantially identical construction and areadapted to be coupled together in any desired spacing and orientationarrangement. Each of the units includes a generally tubular casing,designed to be disposed transversely of the longitudinal axis of thedevice, and is provided with a pair of hollow coupling membersextendingfrom opposite sides of the casing generally along said axis forconnection to the coupling members of adjacent units'forming the series.A detonatable chemical charge having one 3 end hollowed is arranged inthe casing of each unit and each unit is provided with a length ofcord-type detonating fuze, which extends through the casing generallyfrom one` side to the other, the ends of the fuze having knots formedtherein which are seated in the respective coupling members to contactsimilar knots on the ends of the fuzes in adjacent units when severalunits are connected together. The portion of the fuze which passesthrough the interior of the casing is arranged to extend from onecoupling member along one side of the charge toward the end opposite thehollowed end and into detonating contact with this opposite end of thecharge, and thence back along the opposite side of the charge to theopposite coupling member. Detonation-absorbing or cushioning means, suchas strips of a suitable shockabsorbing material, are interposed betweenthe portions of the fuze extending along the sides of the charge tothereby permit only the portion of the fuze passing over the end of thecharge to be in effective detonating contact with this end of thecharge. By this arrangement each charge in a string thereof will, ineffect, be fuzed from the axis of string, thus permitting any desiredorientation of the charges, while, at the same time, each of the chargeswill be effectively detonated from the end thereof opposite the hollowedend, thereby permitting usc of charges of maximum dimensions relative toa particular well bore diameter, whereby to produce optimum jetformation and maximum penetration effectiveness.

Other and more specific objects and advantages of this invention willbecome apparent from the following detailed description when read inconjunction with the accompanying drawings which illustrate embodimentsin accordance with this invention.

Figs-1 and lA together comprise a longitudinal sectional view of aperforating device in accordance with an embodiment of this invention;

Fig. 2 is an enlarged longitudinal sectional view of one of theperforating units;

Fig. 3 is a transverse cross-sectional view along line 3-3 of Fig. 2;

Fig. 4 is a view showing the perforating device suspended in a well inposition to perforate the wall thereof;

Fig. 5 is a longitudinal sectional view of a spacer element forusebetween pairs of perforating units;

Fig. 6 is a detail of another embodiment of a fuze connection betweenunits;

Fig. 7 is a view similar to Fig. 3 of another embodiment of aperforating unit in accordance with this in- Ivention; and Fig. 8 is afragmentary sectional view taken along line 8 8 of Fig. 7.

Referring to the drawings, the perforating device (Fig. l) comprises afiring head 10 to the lower end of which is connected a carrier composedof a plurality of perforating units, each designated generally by thenumeral 11. Firing head 10 is preferably constructed in the form of agenerally cylindrical solid steel body primarily to provide substantialweight to assure ready sinking of the perforating device through anyfluid in the well bore in which it is to be run. Head 10 has a threadedpin 12 at its upper end for connection of a cable connector 13, such asa conventional so-called rope socket, which is carried on the end of alowering cable 14 through which is threaded an electrical conductor 15for transmitting firing current to the firing head from a suitablesource (not shown) of such current located at the surface. Head 10 maybe equipped with a plurality of angularly spaced, upwardly and outwardlysloping flexible wire fingers 16 of generally conventional form (Figs. land 4) which may be employed in the well known manner for locating orpositioning the perforating device lin a well, viz., with reference tothe joints of a casing.

Pin 12 is provided with a tapered bore 17 which is adapted to receive acorrespondingly tapered contact plug 18 having an axially disposedelectrode 19 which is adapted to make electrical connection in the usualmauner to conductor 415 when the rope socket is screwed down on pin 12.An explosive cap 20, of any suitable or conventional type, is supportedin a tubular sleeve 21 attached to the lower end of plug 18, and isarranged in electrical contact with the lower end of electrode 19 sothat it may be fired by electric current supplied through the electrode.A passageway 22 extends axially through head 10 in registration with cap20 and provides communication between the lower end of bore 17 and aninternally threaded socket 23 in the lower end of head 10. A connectorsub 24 having a threaded pin 25 at its upper end is adapted to bescrewed into socket 23 and carries an external packing ring 26, such asa conventional O-ring, below its threaded portion to form a fluidtightseal between the pin and the surrounding wall of socket 23. The lowerend of connector sub 24 is provided with a generally tubularbox 27internally threaded at 28. An axial passage 29 extends through sub 24 inregistration with passageway 22 and communicates with box 27. Anexplosive booster fuze 30, generally comprising a pellet of a suitabledetonating explosive, is aligned with passage 29 and held in position inbox 27 by means of a suitable centralizing bushing 31, which may beconstructed of a suitable insulating material. Fuze 30 is of suicientlength to extend downwardly below the lower face of bushing 31 into box27 as shown.

Connected into box 27 is the first of the series of perforating units11, which are all identical in construction, and the subsequentdescription of one of these units will, therefore, be equally applicableto all of them.

Perforating unit 11 includes a generally tubular casing 32 havingintegrally formed pin and box connections 33 and 34, respectively,extending axially from the opposite sides of the casing at approximatelythe mid-point thereof, which will correspond generally to thelongitudinal axis of the perforating device as a whole. Pin member 33 isexternally threaded and box member 34 is internally threaded. Pin andbox members 33 and 34 are provided with internal sockets `35 and 36,respectively, each of which communicates with the interior of casing 32by means of an axial passageway 37. The base portion of pin member 33has a packing ring 38, also of the conventional O-ring form, mounted inthe periphery thereof to provide a fluid-tight seal between the pinmember and the adjacent wall of a box member in which it may beinserted, as will be described hereinafter.

One end of casing 32 is closed by an outwardly extending, integrallyformed wall 39. The opposite end of casing 32 is open and providedadjacent the open end with an internal annular shoulder 40 adapted toform a seat for a dome-shaped, circular closure cap 41, which isslidably insertible into the open end of casing 32 and provided with anoutwardly curving inner cavity 42. The periphery of cap 41 has acompressible packing ring 43, also of the O-ring form, suitablymountedtherein to form a fluid-tight interior seal with the inner wallof the open outer end of casing 32 when the cap is inserted thereinandseated against shoulder 40.

Disposed within the interior of casing 32 is an explosive charge 44,composed of any suitable high-brisance type of detonating explosivematerial, having a mass and shape to substantially ll thev interior ofthe casing to a point substantially ush with shoulder 40. Charge 44 maybe pr'emolded to the desired size, shape and density, or may be composedof plastic type explosive which may be packed or pressed into theinterior of casing 32 to conform to the internal shape thereof. The endof the charge facing the open end of the casing is provided'with asuitably shaped cavity or hollow 45 which may be generally conical,spherical or other suitable arcuate form..` Hollow 45 is lined with athin liner 46 of corresponding shape, constructed preferably of asuitable metal, such as copper, aluminum, various alloysvthereof, or ofother suitable material. When cap 41 is put in place, it will be Senthat avity'42 forms a sealed hollow chamberfextending forwardly from thehollowed-end of .the charge and Vthis chamber defines the ,so-calledstand-off space .within which the explosive forces are permitted 'toconverge and form into the desired jet conformation without interferencefrom extraneous materials.

A length of a suitable exible fuze cord 47 extends through .the interiorof casing 32 generally transversely thereof. The free ends ofthe cordextend into the opposite passageways 37 and are provided with knots 48formed in the ends which are seated in sockets and 36 of the pin and boxmembers 33 and 34, respectively, forming enlarged masses of detonatablematerial therein which serve as detonation boosters. Portions of thecord extend from the knotted ends rearwardly along opposite sides ofcharge 44, the intermediate portion of the cord being thus arranged Vtopass over and lbe placed in contact with the end ofthe charge oppositethe hollowed end. The portion of cord 47 inside casing 32 is thus heldclosely conned betweenjthe exterior surface of charge 44 and -the innerwall ofthe casing including end wall 39. Strips 49 of a suitableshock-absorbing material, which is preferably a non-metallic material,such as rubber,

lfibrous material or other suitable composition, are inserted betweenthe portions of cord '47 extending along 'the opposite sides of charge44 and the adjacent .portions of the charge. Two of the strips 49 arepreferably employed, each extending lengthwise from a point insidepassageway 37 slightly in advance of the point where the cord kbeginslto bend as it passes into the interior of the casing to a pointslightly spaced from the apex of the rear end of charge 44, to therebyprovide a gap 50 in the shock-absorbing material adjacent the apex ofthe charge, as illustrated particularly in Figs. 2 and 3. Instead of thestrips 491, a `continuous sleeve of shock-absorbing material may beemployed Vtosurround the charge to thereby hold the side portions of thefuze cord out of detonating contact with the sides of the charge. About1/16 inch to Ma inch of shock-absorbing material will ordinarily besuicient for this purpose. .'With the described arrangement only thatportion of ycord 47 which passes over the apex portion of the rear endof charge 44 is in effective detonating Contact with the latter. 'Charge44 may be provided with an arcuate recess'51 in which the cord or atleast the curved inner surface thereof and the interposedshock-absorbing strips are embedded, as shown. Recess 51 maybe preformedin the charge Vduring molding, `or when charge material of .plastic formis pressed or packed into casing 32 with cord 47 in place therein, thepressureemployed in packing the charge will extrude it about the Vcordand strips `to produce the desired ernbedded arrangement. The sides ofpassageways 37 adjacent the points where the cord bends in entering andleaving the interior of casing v32 are smoothly rounded, as at '52, toeliminate sharp corners about which the cord would otherwise be forcedto bend more sharply than is desirable when using lflexible detonatingcord of the general type'described.

Fuze cord47 may Ibe of any suitable or conventional type and ispreferably the material commonly known in the art as Prima Cord, whichis a cord-type material consisting essentially of a flexible tubularcasing, the interior of which Yis packed with a suitable andconventional ydetonating explosive, which is adapted when detonated fromone `end `thereof to transmit a high-powered detonating wave throughoutits length, and may be employed to serially detonate a string ofinter-connected explosive charges such as .are employed in theperforating device herein described.

As previously noted, charge 44 may vbe composed of one or more Vof thewell-known high-brisance types of chemical detonating explosives, whichinclude such materials as pentaerythrytol tetranitrate (PETN),trainitrotoluene (TNT), Pentolite (50% PETN and 50% TNT), TetryL AmatoLCyclouite, Tetrytol (66% Tetryl and TNT), and many yothers well known inthe explosive art. Booster fuze 30 may be composed of similar material.

The several partsof casing 32 and cap 41 are'preferably constructed ofmaterial which will shatter int'o relatively small pieces upon explosionof the charge. Such materials include metallic materials such `asfragile cast iron, cast aluminum or one of its fragile alloys or othermetal `which will withstand high pressures but will also shatterreadily. Special types of glass which are adapted vto withstand high`pressures but which will shatter completely upon explosion of thecharge have been found suitable. Various readily shatterable plasticmaterials may also be used, particularly under relatively low pressureconditions. The material selected wi1l,-in all cases, be such as toproduce as little so-called junk as ,possible in the well which wouldtend to interfere with the 'ow of fiuid into and from the well.

In assembling the perforating device, any 'desirednumber of theperforating units 11 will be connected together, pin member 33 of oneunit being screwed into box 34 of the adjacent unit, thereby forming a'string of units of the desired length. The units may be angularlyoriented with respect to each other to produce any desired pattern ofperforations in the wall of the well. As the units are screwed togetherknots 48 in the adjacent ends of the respective fuze cords will bebrought into compressive contact forming effective connections betweenthe fuze cords of the several units throughout the string of units. Boxmember 34 of the lowermost unit in the string will be closed by means ofa threaded closure plug 53 (Fig. 1) which carries a sealing ring 38ofthe O-ring type to thereby form a 'fluid-'tight seal for the lowermostend of the string of charges. Booster lfuze 30 will be inserted in thelbore of centralizing bushing 31 and sub 24 will be screwed down overpin member 33 of the uppermost unit in the string, thereby insertingfuze 30 into detonating contact with knot 48 `seated in socket 35.Packing ring 3S carried by the base of pin member 33 will compressivelyengage the inner wall of box 27 of the sub to form a fluid-tight sealbetween the pin member and the socket. Pin 2S will then be screwed intosocket 23 to connect the string of perforating units to head 10. Firingplug 18 carrying ring cap 20 will then be inserted into bore 17 and ropesocket "13 will then be connected to pin l12 and the entire device 'willthus be assembled preparatory to lowering into a well bore.

Operation of the device is as follows: The device, assembled as abovedescribed, will be lowered into a well bore 55 (Fig. 4). Merely by wayof illustration, the latter is shown to be partially lined with theusual well casing 56, leaving a section of open hole below the lower endof the casing liner. In this case the device will be lowered until ngers16 are below the end of the casing, whereupon the string will be raisedsufficiently to cause the upper ends of the fingers to engage the lowerend of the casing which thus forms a stop in order to x the position ofthe perforating units opposite the unlined portion of the well bore. Itwill be understood that the device may be positioned within the casing,in cases when it is desired to produce perforations through Vthe casinginto the surrounding formations. In such case fiexible fingers 16 willbe employed in the well known manner to engage in a collar space betweenadjacent sections of the well casing in order to position'theperforating string at the selected point in the well.

When the device is in the Vdesired position in the well bore, currentwill be applied to conductor 15 to set otf cap 20. The jet of hot,highpressure gases released by firing of the cap will travel downwardlythrough passageways 22 and Y29 and will strike booster fuze 30 whichwill be detonated thereby to release a high-velocity detonating wavewhich will strike the adjacent knot 4S of the fuze cord extendingthrough the uppermost one of the perforating units 1'1, and startdetonation of this yfirst section of the fuze cord. The resulting shockwave will travel at a high velocity throughout the length of this rstsection of fuze cord. However, the interposition of shock-absorbingstrips 49 between the fuze cord and charge 44 will effectively preventdetonation of the latter from the side portions of the cord until theshock wave reaches gap S where the cord is in direct contact with thecharge and where the full force of the detonation of the fuze cord willbe applied to the end of the charge. Detonation will thus be effected atthe point on the charge which will produce maximum high-order detonationthereof and most effective jet formation of the explosive forces. Thedetonation wave will then continue through the lower side portion of thefuze cord to lower knot 48 which is in contact with knot 48 of the nextsucceeding perforating unit. The increased mass of detonating materialthus interposed in the path of the detonating wave serves to boost orincrease the velocity of the detonating wave as it enters the fuze cordof the next unit to such a degree as to maintain the velocity of thedetonating wave through the next unit at the same order of magnitude asin the preceding unit and thereby assure equally high-order detonationand jet formation of maximum efficiency of the second unit. The processis repeated throughout the string of perforating units thereby assuringhigh-order detonation and maximum efficiency of jet formation of all ofthe units irrespective of the length of the string.

When the charges have thus been set off, the several perforating units11 will be completely shattered. However, head and the cable connectionswill normally be uninjured and may be withdrawn from the well for reuse.Ordinarily only cap 20 and sub 24 Will need to be replaced, in addition,of course, to a new string of the perforating units.

With the described arrangement it will be seen that all of the chargesare, in effect, fuzed from the common axis of the string thus permittingorientation of the charges about the axis in any desired manner, whileat the same time permitting use of the full length of each charge togive maximum depth of penetration. With such an arrangement the lengthof each charge may be made a maximum for the particular well borediameter in which it is run and thereby permit use of charges which willproduce perforations of maximum size and depth of penetration.

By making the individual units of identical form and dimensions, astring of any desired length and number of charges can be readilyassembled, in'which all of the charges will be uniformly spaced and maybe eifectively detonated from one end in a manner to produce maximumpenetration for each unit. It will be understood that if greater spacingis desired than that which will be produced by connecting one unitdirectly to the other, spacer sleeves of any desired length may beinserted between pairs of the perforating units and a length of fuzecord installed therein to form a fuzing connection between the fuzecords of the connected units. Fig. 5 illustrates an embodiment of aspacing member for effecting such spacing and comprises a tubular sleeve60 of the desired length provided at one end with a hollow threaded pinmember 61 and at the other with a hollow internally threaded box member62, pin member 61 and box member 62 corresponding in dimensions with pinmembers 33 and box members 34 of the units 11. An axial passageway 63extends through sleeve 60 communicating with the interiors of pin andbox members 61 and 62. A length of fuze cord, similar to cord 47, isextended through passageway 63 and is provided with knots 48 at each endseated in the bores of pin and box members 61 and 62.

When such a spacing member is interposed between two of the units 11,the detonation wave will pass from the fuze of one unit to the otherthough the section of cord 47 mounted in sleeve 60 in the same manner asde-.r1

scribed for the directly connected units.

Fig. 6 illustrates another embodiment for boosting the detonation wavepassing from one unit to the next. lIn this embodiment the ends of cord47 are left unknotted and extend into the respective sockets 35 and 36.A pellet of a suitable detonating explosive is inserted between theadjacent ends of the fuze cords of successive perforating units, asshown, and will serve to boost the detonating wave as it passes from onecord section to the other with substantially the same effect as thatproduced by the contacting knots 48.

Figs. 7 and 8 illustrate a somewhat modied embodiment of the perforatingunits, employing pre-molded explosive charges of somewhat modified form,adapted particularly for use in relatively narrow well boresnecessitating the use of charges of relatively small dimensions butwhich will function with maximum penetrative effectiveness.

The explosive charge in this modified embodiment is similar to thatdisclosed in my copending U. S. application, Serial No. 88,740, filedApril 2l, 1949. In this embodirnent, explosive charge 44 is shaped intoa generally conical form by molding or pressing the explosive materialinto a generally conical container 70. Hollow 45 is formed in the largerdiameter end of the charge and is lined with liner 46, as in thepreviously described embodiment. The apex portion of the container isprovided with a transverse notch 71 through which the intermediateportion of fuze cord 47 is threaded. Notch 71 has a relatively thinbottom wall 72 which is curved transversely to conform to the radius ofthe fuze cord and to extend into the interior of the container, so thatwhen the explosive material is pressed into the container it will beextruded around the curved inner surface of bottom wall 72 into thespace between the sides thereof and the adjacent side wall 73 of thecontainer, thereby, in effect, producing a partially embedded relationof the fuze cord to the apex end of the charge (see Fig. 8). Bottom wall72 is also curved outwardly about a relatively large radiuslongitudinally of the notch (Fig. 7) to increase the length of thesurface of bottom wall 72 which is in contact with the fuze cord. Thetapered side wall 73 of the container is made substantially thickerthroughout its circumference than bottom wall 72 and serves the samefunction as strips 49 of the previous embodiment for preventingpre-detonation of the charge from the portions of fuze cord 47 extendingalong the sides thereof toward notch 71. Bottom wall 72 is made to athickness as small as possible so as to readily transmit detonatingshock from cord 47 to the apex portion of the charge and will ordinarilybe from about 5 to 15 one-thousandths of an inch as compared to anaverage thickness of wall 73 of about one-eighth inch. The latterdimension will be such as to interpose a layer of material between theexplosive charge and the adjacent portions of the fuze cord which extendalong the side wall toward the apex portion of the charge, which will besufficient to effectively prevent detonation of the charge by the sideportions of the fuze cord. Container may be constructed of variousmaterials such as one of the numerous synthetic plastics which possesssufcient mechanical strength to support and hold the explosive in thedesired shape and which will permit safe and` effective handling of thecharge and container as a unit for shipping and loading. Such materialswill also be readily destroyed by the explosion of the charge. Due tothe conical conformation of container 70 some air space, indicated at74, may also be provided between the sides of the container and theadjacent portions of the fuze cord to thereby additionally protect theside portions of the charge from the detonating wave traversing cord 47.

I have discovered that the diameter of the perforation made by aperforating unit, of any given size, in accordance with this invention,may be controlled to an important degree, merely by the selection of thematerial from which cap 41 is constructed. For example, ifcap 41 isconstructed of cast iron, a substantially larger perforation will beproduced than when the cap is made of aluminum alloys, using identicalexplosive charges, and without any other changes in the size, form,material, and fuzing arrangement of the unit as a whole. Thus, standardperforating units of a given size may be employed to make various sizedperforations, as desired, merely by supplying caps 41 constructed ofdifferent materials, thereby avoiding the necessity, in many cases, ofproviding a dierent size perforating unit for each particular size ofperforation which is desired.

lt will be understood that the perforating gun may be run on a wire lineor string of tubing and tiring head modilied in accordance withconventional practice to permit ring of cap by well-known mechanicalpercussion methods, as the electrical tiring arrangement illustrated anddescribed herein is presented merely by way of example.

Numerous other alterations and modilications may be made in the detailsof the illustrative embodiments without departing from the scope of theappended claims but within the spirit of this invention.

What I claim and desire to secure by Letters Patent 1s:

1. An explosive unit for a well perforating device, cornprising, adetonatable chemical charge having one end hollowed, a casing enclosingsaid charge, a continuous detonating fuze extending generallytransversely through said casing and having an intermediate portionextending transversely across and in detonating contact with theopposite end of said charge and having its other portions extending fromsaid intermediate portion along opposite sides of said charge betweenthe charge and the wall of said casing to points intermediate said ends,detonationabsorbing means comprising strips of a shock-absorbingmaterial interposed between said other portions and adjacent portions otsaid charge, and detonation-boosting elements carried by the oppositefree ends of said fuze disposed for detonating engagement withdetonating ele ments of adjacent units.

2. An explosive unit for a well perforating device, comprising, adetonatable chemical charge having one end hollowed, a casing enclosingsaid charge, a continuous cord-type detonating fuze extending generallytransversely through said casing and having an intermediate portionextending transversely across and in detonating contact with theopposite end of said charge and having its other portions extending fromsaid intermediate portion along opposite sides of said charge betweenthe charge and the wall of said casing to points intermediate said ends,detonation-absorbing means interposed between said other portions andadjacent portions of said charge, and detonation-boosting elementscomprising knots formed in the opposite free ends of said fuze disposedfor detonating engagement with detonating elements of adjacent units.

3. A well perforating device, comprising, a carrier designed forplacement in a well and embodying a ring head and a series ofsubstantially identical separable perforating units connected at one endto said head, each of said perforating units comprising a generallytubular casing arranged transversely of the longitudinal axis of saidcarrier and having hollow coupling elements extending from oppositesides thereof along said axis, a detonatable chemical charge having oneend hollowed Co-axially disposed in said casing, a continuous length ofdetonating fuze extending generally transversely through said casinghaving an intermediate portion thereof extending transversely across andin detonating contact with the opposite end of said charge and its otherportions extending along opposite sides of said charge and terminatingwithin said coupling elements, detonation-absorbing elements interposedbetween said other portions and adjacent portions of said charge, anddetonation-boosting elements carried by the free ends of said fuzeextending into said coupling elements and into contact with the boostingelements on the fuzes of adjacent units.

4. An explosive unit for a well perforating device, cornprising, agenerally cylindrical detonatable chemical charge having one endhollowed, a generally tubular casing concentrically enclosing saidcharge, hollow connection members extending laterally from oppositesides of said casing intermediate the ends thereof and communicatingwith the interior thereof, a single length of a cordtype detonating fuzeextending generally transversely through said casing, said fuze havingan intermediate portion extending transversely across and in detonatingcontact with the end ot said charge opposite said hollowed end andhaving its opposite ends extending into and terminating within saidconnection members, and knots formed in both the opposite free ends ofsaid fuze.

5. An explosive unit according to claim 4 having detonation-absorbingmeans interposed between said charge and the portions of said fuzeextending from the opposite ends of said intermediate portion of saidfuze.

6. An explosive unit according to claim 4, wherein said connectionmembers are provided with threaded sections for threaded connection tosimilar adjacent units.

7. An explosive unit according to claim 4 having a removable closure forthe end of said casing adjacent the hollowed end of said charge.

References Cited in the le of this patent UNITED STATES PATENTS1,968,565 Mallet July 31, 1934 2,026,061 Prikel Dec. 31, 1935 2,139,104Wells Dec. 6, 1938 2,391,932 Turechek Jan. 1, 1946 2,402,153 ElliottJune 18, 1946 2,414,349 Alexander Jan. 14, 1947 2,418,486 Smylie Apr. 8,1947 2,446,235 Markham Aug. 3, 1948 2,494,256 Muskat Jan. 10, 1950

